pyxl320 0.5.2

A library to control dynamixel XL-320 servos with python

This is still a work in progress and only supports XL-320 and only version 2.0 of their protocol.

The library is divided up as follows:

• pyxl320

  • ServoSerial - half duplex hardware serial interface

  • DummySerial - for testing, doesn’t talk to any hardware

  • Packet - creates packets

  • utils - misc

  • xl320 - register/command/error definitions for Dynamixel’s XL-320 servo

Not everything is implemented, but more will be added over time.

Setup

Install

pip install pyxl320

Development

To submit git pulls, clone the repository and set it up as follows:

git clone https://github.com/walchko/pyxl320
cd pyxl320
pip install -e .

Usage

from pyxl320 import xl320
from pyxl320 import ServoSerial, Packet, utils

serial = ServoSerial('/dev/tty.usbserial')  # tell it what port you want to use
serial.open()

pkt = Packet.makeServoPacket(1, 158.6)  # move servo 1 to 158.6 degrees
serial.write(pkt)  # send packet to servo
ans = serial.read()  # get return status packet

if packet.isError(ans):
        pkt = packet.makeLEDPacket(1, pyxl320.XL320_LED_RED)
        serial.write(pkt)
        raise Exception('servo error: {}'.format(packet.errorString(ans)))

Al though I have made some packet creators (like LED and Servo), you can make your own using the basic makeWritePacket and makeReadPacket.

from pyxl320 import Packet, xl320
from pyxl320.Packet import le  # creates little endian numbers

# let's make our own servo packet that sends servo 3 to 220.1 degrees
ID = 3
reg = xl320.XL320_GOAL_POSITION
params = le(int(220.1/300*1023))  # convert 220.1 degrees to an int between 0-1023
pkt = Packet.makeWritePacket(ID, reg, params)

Packet Basics

Header	ID	Length	Instruction	Parameter	CRC
[0xFF, 0xFF, 0xFD, 0x00]	ID	[LEN_L, LEN_H]	INST	[PARAM 1, PARAM 2, …, PARAM N]	[CRC_L, CRC_H]

A status packet back from the servo follows the same format, but the instruction is always 0x55 and maybe followed by error codes if something is wrong. The length of the packet is aways the entire length minus header, id, and crc. Also remember, the packets are little-endian, so place numbers in the packet as [LSB, MSB]. You can use the function le() in Packet to accomplish this.

See the references below for more details on the instructions, error codes, etc.

Hardware

References:

Unfortunately the Dynamixel references below are not written well (many typos and errors throughout), so please be careful or you will exhibit much frustration.

• XL-320 e-Manual

• XL-320 hardware and half duplex circuit

• Dynamixel Protocol Ver. 2

• PySerial

ToDo

• look at using python struct for packets

• clean up packet reading, sometimes get a 0 appended at beginning or end

• look at using a class system instead of functions for packets

• look at setting up a servo based on a json file

• more helper functions in utils and or bin

Change Log

2016-09-05	0.5.0	published to PyPi
2016-08-16	0.0.1	init